In the automated production of contact lenses in general, but especially in the production of large batches of contact lenses, as is the case for example with disposable contact lenses, it is necessary at certain stations in the production process to be able to manipulate the contact lenses safely, quickly and efficiently. An example of such manipulation of a contact lens is when the contact lens is removed from a test cell in which said contact lens has been placed in a liquid, for example in water, in order to inspect it (e.g. by image processing).
To remove the inspected contact lens from the test cell known devices called grippers are typically used. Grippers are also used at other stations in such automated production process. The contact lens is gripped with the aid of the gripper, and in the example described above the gripper together with the gripped contact lens is removed from the test cell. The gripper together with the contact lens is then moved, for example, to a receptacle which can be part of the final package for the contact lens and into which a storage solution (e.g. saline) has been or will be dispensed. The contact lens is then released from the gripper and deposited in the receptacle. The receptacle is then covered with a foil which is later on welded or sealed to the receptacle, and after subsequent autoclaving the final package can be distributed.
In the above-described removal of the contact lens from the test cell, or other environment from which it is removed, and the subsequent dispensing of the contact lens into a receptacle in which a saline is (or will be) present, care must be taken to ensure that only a very small amount of water, preferably no water at all, is entrained with the contact lens, otherwise the saline may become diluted. This is a problem which is not at all easy to solve, because the contact lens in the above-mentioned test cell has to be sucked from “under water” (with the result that water is necessarily also sucked out with the lens), then transported to the receptacle which is part of the final package, and finally deposited in this receptacle, for which purpose the contact lens has to be released again from the gripper. In addition, the contact lens has to be gripped securely by the gripper (even “under water”), and in the case of small receptacles the contact lens has to be reliably deposited in the receptacle so that it cannot later get damaged during the welding or sealing of the cover foil.
A gripper suitable to fulfill these requirements is known from WO 2011/026868 A1. Removal of the contact lens from the bearing surface of this gripper is accomplished by discontinuing the underpressure and by applying overpressure through the suction openings in the bearing surface. Due to the overpressure applied through the suction openings the contact lens is blown off the bearing surface. However, care must be taken in controlling the overpressure to ensure that the air flow through the suction openings in the bearing surface of the gripper does not have an adverse effect on the storage solution contained in the receptacle or on the contact lens deposited in the receptacle. For example, if too high an overpressure is applied the storage solution (e.g. saline) which has been dispensed into the receptacle before, may at least partially be blown out of the receptacle. This may lead, for example, to problems in the subsequent welding or sealing of the cover foil to the receptacle, since droplets blown out of the receptacle may deposit in the area where the cover foil is to be sealed to the receptacle, so that welding or sealing may be incomplete. Or, in an even worse case the contact lens itself may be blown out of the receptacle.
On the other hand, in case too low an overpressure is applied the contact lens may not be completely released from the gripper but instead may at least partially adhere to the bearing surface of the gripper. In both cases, if a contact lens has been blown out of the receptacle or if it has not been completely released from the gripper despite the application of overpressure, no contact lens is contained in the receptacle so that the welded or sealed package does not contain a contact lens. Such package and any additional packages connected to such package (for example when being sealed by a common foil extending over a plurality of packages) must be sorted out and discarded, and cannot be distributed. In addition, when the contact lens has not successfully been released from the bearing surface and the gripper subsequently returns to its starting position to grip (suck) another contact lens, it may be unable to grip the next contact lens since the previously gripped contact lens still adheres to the bearing surface.
Therefore, there exists a need to ascertain that a contact lens gripped by a gripper at a starting location is safely released from the bearing surface of the gripper at a destination location. Concurrently, adverse effects due to too high an overpressure or due to too low an over-pressure applied through the suction openings in the bearing surface of the gripper shall be avoided.